ideally center of the roof is best, so above the inside light. but we install most of them just a couple inches in front of the rear brake light for ease of install, at least if it is VHF/UHF/700/800 mhz anyway. for low band it just about has to go centered. just undo the 2 screws and let the light hang. drill your hole, drop in the line and work it out past the bottom edge of the liner. then feed it around the edge and tuck it under. when you get to the front bring it down behind the weather stripping and feed it under the dash and across. i prefer to come across on the passenger side so i know it won't get near the steering shaft, but if you do come across on driver's side just make sure you tie wrap it in place good so it cant get wrapped in the shaft.